1. Field
The following description relates to a signal processing technology of a terrestrial repeater that transmits a satellite signal to a user terminal.
2. Description of the Related Art
In recent years, with the development of the communication technology, a satellite communication system has been developed to provide a user terminal on the move with various types of signals such as video data and audio data through a satellite.
Satellite communication and broadcast services basically require a line of sight (LOS) environment, and a user terminal may have a difficulty in directly receiving a satellite signal due to a shadow phenomenon in a urban area. For this reason, a terrestrial reaper is used.
As an example of satellite communication system using a repeater, a Digital Multimedia Broadcasting (DMB) developed in Korea and a Satellite-Digital Multimedia Broadcasting (S-DMB) developed in Europe have been proposed. A repeater in the Korea DMB is defined as a gap filler, and a repeater in the Europe S-DMB is defined as an Intermediate Module Repeater (IMR).
The repeater implemented in the current satellite communication system is divided into a simple amplification repeater and a frequency conversion repeater. The simple amplification repeater amplifies a received satellite signal on the same frequency and relays the amplified signal to a user terminal. The frequency conversion repeater performs a frequency conversion and amplification on a received satellite signal and relays the signal to the user terminal.
As described above, conventional terrestrial repeater is implemented to perform simple frequency conversion and signal amplification. However, in recent years, there are provided technologies in which various types of additional functions are added to the conventional terrestrial repeater to provide improved performance and services. In particular, there is a technology in which a terrestrial repeater performs an additional signal processing using additional error correction code (ECC) and Space-Time Code (STC) and thus a terminal combines a satellite signal to a signal that is processed in a repeater to obtain a diversity gain.
As described above, in the satellite communication system, a user terminal may directly receive from a satellite directly or may indirectly receive through multiple repeaters from a satellite directly. A signal directly received from the satellite and a signal received through the repeaters may go through different channel environments while reaching the terminal. In this condition, the terminal may improve the reception performance by use of the diversity technology for receiving multiple signals from the satellite and the repeaters simultaneously.
In addition, the satellite transmits information to the terrestrial repeater in a high order modulated symbol, and transmits information to the user terminal in a low order modulated symbol. In this case, if the terminal has a capability to receive the signal from the terrestrial repeater, the terminal has high quality of services, if the terminal can only receive the satellite signal, the terminal has basic quality of services.
There is a need for maximizing the frequency utilization by enhancing the efficiency of spectrum in consideration of the service providing environment by each of the terrestrial repeater and the satellite.